org.jwat.gzip:

The standard GZip classes in the Java runtime library do not directly support a file with multiple compressed entries. They do however support the raw deflation of an inflated stream without reading a GZip header.

GzipInputStream.java

This is the main class used to read GZip entries. It is instantiated like a normal InputStream but has some additional methods to read the next record and get the entry content as an InputStream.